I did the 4 1/4 at first and realized it had to be 4.5 inches. I made two blocks with scraps from the twin quilt just to practice. Had trouble with the corners matching, but with reattempts got them to work as best as I could. Used two left over blocks that were extra (wrong size etc) for quilt and did some cutting to make it all work together, but have already finished it complete with batting, backing, quilting and edge. It's hanging on the wall. My third quilt! My first 'scrappy'!
I'll try to post photo.

Scrappy quilt wall hanging, Not real square so not sure what I did wrong.

THANKS to everyone who responded..........My daughter really liked the look of the blocks with this method - using reds, blues and a nice sandy tan for the 4.5 inch lighter piece (many of the prints have that sandy tan color in them). The squares looked really nice when laid out.........but I was concerned before I started sewing - wanted to make sure I was doing it correctly.

Really appreaciate the help............she wants me to do all of the small blocks first, and then let her "play" on the design wall to decide how she wants them put together.....This will be a king sized quilt for her master bedroom.

To eliminate the pt. problem, lay the 45 degree line of your ruler on the long cut edge of the fabric, not on the sewn seam. The top point of the ruler should be on the stitching line at the top.

If you use two 2 1/2" strips sewn together, your sewn strip is 4 1/2" wide. (the video says 4 1/4" but NOT)

If you use the width of the fabric on the 2 1/2" strips you should get 10 cuts (HS triangle blocks). So you'll get 2 complete blocks with 2 extra cuts. I thought I'd use my extra cuts in the borders somehow.

I've been sick for the past 10 days but will try to get some pictures posted back on the original post.

Yep, did that last night. I found my lovely blues and browns and made some blocks. i laid my 45 degree of my 6 1/2 inch ruler on the raw edge. i ended up with 6 inch squares and would have had 12 inch blocks but I needed them to be 8 inches, so i had to cut down each one to 4 1/2. i'm not done making blocks so i must remember exactly how i trimmed them so they all will match up.
i'm covering an ottoman. i need two blocks across and four down the length. 16x32. then my cats can lay on it all they want. mamma cat has loved it so much and jumped onto it from her tree perch that she's made some claw holes in it! So a quilt to the rescue. I can always make another when necessary.

I cut out a few and had no trouble with the points when I followed the instructions precisely.. her math does suck.. and if you listen carefully she says to stitch the strips end to end.. and I believe she stitches them side to side.. to me the cut edge is the side and the selvedge is the end. I used my 6.5 x 23" ruler. Worked fine!